For conditions that must be treated by delivering drugs through the blood stream, medical science has developed new drugs that cannot be delivered to the blood via the stomach because acids and enzymes of the stomach will destroy them. Examples of such drugs include protein drugs, drugs made with peptide molecular groups, and vaccines. These drugs must be delivered by injection or by absorption through mucous membranes, such as mucous membranes of the mouth, nose, or vagina. For delivery in the mouth, it is known to put such drugs in a dissolving tablet or lozenge or film that is held in the mouth until the delivery vehicle has dissolved. With this delivery method, a large portion of the delivered drug will be swallowed down the throat along with saliva and that portion is wasted. For drugs that are inexpensive and the range of suitable dosage is wide, such as vitamin B12, one can merely provide enough quantity of the drug that the portion absorbed through the mucosal membranes of the mouth provides a sufficient dose. However, for expensive drugs that cannot be delivered through the stomach, the waste increases cost too much for practical use. And this method can not be used where the suitable dosage range requires greater precision because a large portion will go down the throat one time but not another time.
Also, for drugs that should be delivered via a muco-adhesive patch to a single spot in the mouth, the action of the muco-adhesive drawing water from a spot can prevent the drug from diffusing into the spot.
The first muco-adhesive oral patch was made by pressing grains into a thin, wide tablet. The tablet can be made to adhere on only one side by first pressing into a tablet die a small amount of powder and then adding more powder of a different composition and pressing again. Canker Cover, sold by Quantum, is an example. Orajel (“Protective Mouth Sore Discs”) improved the shape by making each side domed and making the edge as thin as possible to produce a lenticular shape. However, a thin edge is inconsistent with multiple layers.
Pressing grains into a tablet can never make a patch that is flexible and yet strong enough not to fall apart because there are no fibers or polymer strands that cross grain boundaries. If the grains become elastic enough to flex, due to heat or moisture, the grains will pull apart from each other.
Pressing grains into a tablet also can not produce a thin, tapered edge. There must always be a substantial straight vertical “cliff” edge to the tablet because the machines that make them must have the flexibility to produce a range of thicknesses in each tablet to ensure that adequate pressure is applied. In other words, the thickness of the edge must be determined by achieving the proper pressure, not by the final thickness dimension, which requires that the edge thickness vary according to the exact amount and composition of the powders put into the press for each tablet. The Orajel patch was produced with the thinnest edge practical by tablet pressing, about 0.75 mm, which is about 30 thousandths of an inch. To press a tablet with two layers requires a cliff edge at least twice this thick.
The only solution to the problem of strength with flexibility described above is to mix the preferred ingredients together in a liquid and then cure it to a solid. The mixture will include long polymer molecules, some of which may be organized into fibers. The curing may be accomplished by cooling or by evaporating a solvent or both.
In a prior art method implementing this solution, the preferred ingredients are mixed together and heated to a liquid, then formed to a sheet, and then cooled. Because long chain molecules can be intertwined with no grain boundaries, it is strong yet can be flexible. The sheets can be formed by pouring onto a flat table, like making glass, or can be rolled or extruded. Layers can be separately formed and then bonded together or can be co-extruded. The sheet is then die cut into patches of the preferred shape.
Like the tablet press method, the die-cut sheet method can not produce a thin, tapered edge. The edges of the patch cut by the die are vertical “cliff” edges. Nor can it produce a lenticular shape. Both sides are flat.